1. Field of the Invention
This invention relates to a wear-detection probe for a brake lining material such as a brake pad for a disc brake in a vehicle or the like.
2. Statement of the Prior Art
For convenience of explanation, a conventional wear-detection probe for brake lining material will be described below by referring to FIGS. 5 through 9.
FIG. 5 is a side view showing a conventional disc brake for a vehicle.
As shown in FIG. 5, a disc brake 1 for a vehicle generates a braking force by pressing a pair of brake lining materials such as brake pads 3 or the like on both sides of a rotor 2 which rotates in connection with the rotation of the wheels. In this disc brake 1, a probe 10 juxtaposed with the brake pad 3 detects the residual thickness of the pad 3 worn by contact with the rotor 2, so that a warning signal can be generated before the brake pads are overworn.
FIG. 6 is a plan view of a conventional wear-detection probe 10 for a brake pad 3. FIG. 7 is a cross-sectional view taken along lines VII--VII in FIG. 6. FIG.8 is a perspective view of the conventional probe shown in FIG. 6. The probe 10 comprises a housing 13 molded by a resin material 12, an insulated electrical wire 11, and a detector K having a U-turned portion 11a of the wire 11. The U-turned portion 11a is embedded in the resin material 12.
The probe 10 is secured to the rear metal 3a of the brake pad 3 at a flange 10b so that the top end 10a of the probe 10 is directed to the rotor 2 and both ends of the insulated electrical wire 11 are drawn out of the probe 10 so as to be connected to an alarm circuit (not shown). The brake pad 3 is worn due to contact with the rotor 2 every time the brake is operated, and the top end 10a of the probe 10 is also worn with reduction of the residual thickness of the brake pad 3. Consequently, the U-turned portion 11a is gradually worn. When the residual thickness of the brake pad reaches a predetermined value, the U-turned portion 11a is cut off. The alarm circuit detects the disconnection of the U-turned portion and generates a warning signal.
Thus, since a wear limit of the residual brake pad 3 is detected by the disconnection of the U-turned portion 11a, it is necessary to accurately position the U-turned portion 11a in the resin material 12, in particular, in a wear-progressing direction A (see FIG. 6) with respect to the residual thickness of the brake pad 3.
Accordingly, in a conventional method of producing the probe 10, as shown in FIG. 9, first, the insulated electrical wire 11 is disposed around a pin 20 mounted in a mold (not shown) to form the U-turned portion 11a, and second, a molten resin material is poured into the mold while holding the wire by the pin 20 so that the wire does not shift in the mold. The resin material solidifies in the mold so that the electrical wire 11 is correctly positioned in the molded resin material 12.
However, after molding the probe 10, a hole 21 (see FIGS. 6 through 8) is left inside the U-turned portion 11a in the housing 13 by drawing the pin 20 out of the resin material 12. Consequently, the probe 10 is weakened near the detector K. If a pushing force F (see FIG. 6), caused by contact with the rotor 2, is applied to the top end 10a of the probe 10, the probe is easily broken, or the U-turned portion 11a is deflected into the hole 21, thereby displacing the disconnection position of the U-turned portion 11a.
Although it is possible to increase the strength of the probe 10 and to prevent the deflection of the U-turned portion 11a by filling the hole 21 with a resin material, this filling material increases the number of parts and the steps of producing the probe.